[RFC PATCH v2 21/28] cxl/acpi: Handle address space allocation

[Ben Widawsky <ben.widawsky@intel.com>]

Regions are carved out of an addresses space which is claimed by top
level decoders, and subsequently their children decoders. Regions are
created with a size and therefore must fit, with proper alignment, in
that address space. The support for doing this fitting is handled by the
driver automatically.

As an example, a platform might configure a top level decoder to claim
1TB of address space @ 0x800000000 -> 0x10800000000; it would be
possible to create M regions with appropriate alignment to occupy that
address space. Each of those regions would have a host physical address
somewhere in the range between 32G and 1.3TB, and the location will be
determined by the logic added here.

The request_region() usage is not strictly mandatory at this point as
the actual handling of the address space is done with genpools. It is
highly likely however that the resource/region APIs will become useful
in the not too distant future.

All decoders manage a host physical address space while active. Only the
root decoder has constraints on location and size. As a result, it makes
most sense for the root decoder to be responsible for managing the
entire address space, and mid-level decoders and endpoints can ask the
root decoder for suballocations.

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
---
 drivers/cxl/acpi.c | 30 ++++++++++++++++++++++++++++++
 drivers/cxl/cxl.h  |  2 ++
 2 files changed, 32 insertions(+)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index 23afb3b8f5cc..65219b18f3bc 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2021 Intel Corporation. All rights reserved. */
 #include <linux/platform_device.h>
+#include <linux/genalloc.h>
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
@@ -75,6 +76,27 @@ static int cxl_acpi_cfmws_verify(struct device *dev,
 	return 0;
 }
 
+/*
+ * Every decoder while active has an address space that it is decoding. However,
+ * only the root level decoders have fixed host physical address space ranges.
+ */
+static int cxl_create_cfmws_address_space(struct cxl_decoder *cxld,
+					  struct acpi_cedt_cfmws *cfmws)
+{
+	const int order = ilog2(SZ_256M * cxld->interleave_ways);
+	struct device *dev = &cxld->dev;
+	struct gen_pool *pool;
+
+	pool = devm_gen_pool_create(dev, order, NUMA_NO_NODE, dev_name(dev));
+	if (IS_ERR(pool))
+		return PTR_ERR(pool);
+
+	cxld->address_space = pool;
+
+	return gen_pool_add(cxld->address_space, cfmws->base_hpa,
+			    cfmws->window_size, NUMA_NO_NODE);
+}
+
 static void cxl_add_cfmws_decoders(struct device *dev,
 				   struct cxl_port *root_port)
 {
@@ -133,6 +155,14 @@ static void cxl_add_cfmws_decoders(struct device *dev,
 		cxld->interleave_granularity =
 			CFMWS_INTERLEAVE_GRANULARITY(cfmws);
 
+		rc = cxl_create_cfmws_address_space(cxld, cfmws);
+		if (rc) {
+			dev_err(dev,
+				"Failed to create CFMWS address space for decoder\n");
+			put_device(&cxld->dev);
+			goto next;
+		}
+
 		rc = cxl_decoder_add(cxld, target_map);
 		if (rc)
 			put_device(&cxld->dev);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 430de5ab805a..509b20375e0e 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -225,6 +225,7 @@ enum cxl_decoder_type {
  * @target_type: accelerator vs expander (type2 vs type3) selector
  * @flags: memory type capabilities and locking
  * @region_ida: allocator for region ids.
+ * @address_space: Used/free address space for regions.
  * @nr_targets: number of elements in @target
  * @target: active ordered target list in current decoder configuration
  */
@@ -237,6 +238,7 @@ struct cxl_decoder {
 	enum cxl_decoder_type target_type;
 	unsigned long flags;
 	struct ida region_ida;
+	struct gen_pool *address_space;
 	const int nr_targets;
 	struct cxl_dport *target[];
 };
-- 
2.33.1